A variety of constructions have hitherto been proposed for increasing the gain of single-element antennas. FIGS. 30A and 30B shows an example of the structure of a microstrip antenna having a metal wall, which is one construction that has been investigated as a way of increasing the gain of single-element antennas (see Patent Document 1). FIGS. 30A and 30B are respectively perspective and cross-sectional views showing the construction of a conventional antenna device. In FIGS. 30A and 30B, 15 denotes a cylinder, 16 denotes a microstrip patch, 17 denotes a feeding point, 18 denotes a substrate, 19 denotes a ground plate, 20 denotes a substrate for feeding circuit, and 21 denotes a feeding circuit.
The scheme is shown which increases the gain of a microstrip antenna by providing a cylinder 15, being a metal wall, as the basic configuration. Specifically, the construction here is one in which a cylinder 15 made of metal is placed around a microstrip antenna composed of a substrate 18, a microstrip patch 16 formed on the substrate 18, and a ground plate 19 provided on the back surface of the substrate 18. The cylinder 15 is grounded to the ground plate 19 of the microstrip antenna.
Patent Document 1: Japanese Patent No. 3026171